Asthma is the most common chronic disease in children. Epidemiologic evidence suggests that asthma begins in early life and even prior to birth, with risk profiles established during the first few years of life. Although many prenatal an early life exposures have been implicated in risk for asthma, no studies to date have integrated prenatal (maternal) and early life exposures in the child with longitudinal changes in epigenetic and gene expression profiles, microbiome composition, and genetics with clinical outcomes, including the development of asthma in the child. In this application, we propose to harness the wealth of information already collected as part of the 2010 COpenhagen Prospective Study on Asthma in Childhood (COPSAC2010) and further extend the mechanistic scope of those studies with genome-wide assessments of DNA methylation and gene expression at birth, 18 months and 6 years. These rich data will afford us the unique opportunity to pursue the following three specific aims. In Aim 1 we will investigate the impact of maternal exposures during pregnancy on the child's immune and airway development in the first 6 years of life and determine whether these relationships differ in children of mothers with or without asthma. We will consider prenatal exposures that have been implicated in asthma risk, such as maternal asthma, vaginal microbiome, diet, and mode of delivery, among others, and clinical and immunological outcomes in the child, including longitudinal measures of the child's gut, skin and airway microbiome, DNA methylation and gene expression levels in blood cells, early life wheezing, asthma by age 6, exacerbations, lung function and allergic disease. In Aim 2, we will determine how maternal supplementation during pregnancy with fish oil or placebo in a randomized controlled trial affects the child's immune and airway development in the first 6 years of life, an whether these effects differ in children of mothers with or without asthma or interact with other risk factors identified in Aim 1. In Aim 3, we will elucidate interaction effects of maternal exposures in pregnancy (including maternal asthma and fish oil supplementation) and child's genotype at asthma/allergy candidate loci on the occurrence of persistent wheeze in the first 3 yrs. of life, exacerbations, allergic disease, and the development of asthma by age 6. In this aim we will integrate significant findings from Aims 1 and 2 with genotype at known risk loci to identify variants that modify the child's response to relevant environmental exposures, and their associations with DNA methylation and gene expression as well as clinical outcomes. All 3 aims will fill a major gap in the field by developing methods for integrating multiple high-dimensional data sets. The proposed research will contribute to the mechanistic understanding of the prenatal origins of asthma through the integration of detailed data on exposures during pregnancy, longitudinal measures of clinical and immunological outcomes in the child, and gene regulatory processes and genotypes at asthma/allergy risk loci in the child. Our studies will likel lay the foundation for development of novel treatments, biomarkers and preventive strategies for childhood asthma.